Electronic battery tester

ABSTRACT

An electronic battery tester for determining a condition of a storage battery includes a forcing function adapted to couple to the battery. Circuitry coupled to the forcing function is adapted to obtain measurements from the battery at multiple levels of the forcing function. In the method according to the present invention, a forcing function is applied to the battery at a first level and a first measurement is obtained. The forcing function is applied at a second level and a second measurement is obtained. The first and second measurements are correlated to condition of the battery.

The present invention claims priority to Provisional Application Ser.No. 60/132,045, filed Apr. 30, 1999, and entitled ELECTRONIC BATTERYTESTER.

BACKGROUND OF THE INVENTION

The present invention relates to testing of storage batteries. Morespecifically, the present invention relates to testing storage batteriesusing conductance, impedance, resistance, admittance or theircombination.

Storage batteries, such as lead acid storage batteries of the type usedin the automotive industry, have existed for many years. However,understanding the nature of such storage batteries, how such storagebatteries operate and how to accurately test such batteries has been anongoing endeavor and has proved quite difficult. Storage batteriesconsist of a plurality of individual storage cells electricallyconnected in series. Typically each cell has a voltage potential ofabout 2.1 volts. By connecting the cells in series, the voltages of theindividual cells are added in a cumulative manner. For example, in atypical automotive storage battery, six storage cells are used toprovide a total voltage when the battery is fully charged of 12.6 volts.

There has been a long history of attempts to accurately test thecondition of storage batteries. A simple test is to measure the voltageof the battery. If the voltage is below a certain threshold, the batteryis determined to be bad. However, this test is inconvenient because itrequires the battery to be charged prior to performing the test. If thebattery is discharged, the voltage will be low and a good battery may beincorrectly tested as bad. Furthermore, such a test does not give anyindication of how much energy is stored in the battery. Anothertechnique for testing a battery is referred as a load test. In a loadtest, the battery is discharged using a known load. As the battery isdischarged, the voltage across the battery is monitored and used todetermine the condition of the battery. This technique requires that thebattery be sufficiently charged in order that it can supply current tothe load.

More recently, a technique has been pioneered by Dr. Keith S. Champlinand Midtronics, Inc. for testing storage batteries by measuring theconductance of the batteries. This technique is described in a number ofUnited States patents, for example, U.S. Pat. No. 3,873,911, issued Mar.25, 1975, to Champlin, entitled ELECTRONIC BATTERY TESTING DEVICE; U.S.Pat. No. 3,909,708, issued Sep. 30, 1975, to Champlin, entitledELECTRONIC BATTERY TESTING DEVICE; U.S. Pat. No. 4,816,768, issued Mar.28, 1989, to Champlin, entitled ELECTRONIC BATTERY TESTING DEVICE; U.S.Pat. No. 4,825,170, issued Apr. 25, 1989, to Champlin, entitledELECTRONIC BATTERY TESTING DEVICE WITH AUTOMATIC VOLTAGE SCALING; U.S.Pat. No. 4,881,038, issued Nov. 14, 1989, to Champlin, entitledELECTRONIC BATTERY TESTING DEVICE WITH AUTOMATIC VOLTAGE SCALING TODETERMINE DYNAMIC CONDUCTANCE; U.S. Pat. No. 4,912,416, issued Mar. 27,1990, to Champlin, entitled ELECTRONIC BATTERY TESTING DEVICE WITHSTATE-OF-CHARGE COMPENSATION; U.S. Pat. No. 5,140,269, issued Aug. 18,1992, to Champlin, entitled ELECTRONIC TESTER FOR ASSESSING BATTERY/CELLCAPACITY; U.S. Pat. No. 5,343,380, issued Aug. 30, 1994, entitled METHODAND APPARATUS FOR SUPPRESSING TIME VARYING SIGNALS IN BATTERIESUNDERGOING CHARGING OR DISCHARGING; U.S. Pat. No. 5,572,136, issued Nov.5, 1996, entitled ELECTRONIC BATTERY TESTER WITH AUTOMATIC COMPENSATIONFOR LOW STATE-OF-CHARGE; U.S. Pat. No. 5,574,355, issued Nov. 12, 1996,entitled METHOD AND APPARATUS FOR DETECTION AND CONTROL OF THERMALRUNAWAY IN A BATTERY UNDER CHARGE; U.S. Pat. No. 5,585,728, issued Dec.17, 1996, entitled ELECTRONIC BATTERY TESTER WITH AUTOMATIC COMPENSATIONFOR LOW STATE-OF-CHARGE; U.S. Pat. No. 5,592,093, issued Jan. 7, 1997,entitled ELECTRONIC BATTERY TESTING DEVICE LOOSE TERMINAL CONNECTIONDETECTION VIA A COMPARISON CIRCUIT; U.S. Pat. No. 5,598,098, issued Jan.28, 1997, entitled ELECTRONIC BATTERY TESTER WITH VERY HIGH NOISEIMMUNITY; U.S. Pat. No. 5,757,192, issued May 26, 1998, entitled METHODAND APPARATUS FOR DETECTING A BAD CELL IN A STORAGE BATTERY; U.S. Pat.No. 5,821,756, issued Oct. 13, 1998, entitled ELECTRONIC BATTERY TESTERWITH TAILORED COMPENSATION FOR LOW STATE-OF-CHARGE; and U.S. Pat. No.5,831,435, issued Nov. 3, 1998, entitled BATTERY TESTER FOR JISSTANDARD.

However, there is an ongoing need to improve battery testing techniquesand derive additional information about the battery using non-invasiveelectrical means.

SUMMARY OF THE INVENTION

An electronic battery tester for determining a condition of a storagebattery includes a forcing function adapted to couple to the battery.Circuitry coupled to the forcing function is adapted to obtainmeasurements from the battery at multiple levels of the forcingfunction. In the method according to the present invention, a forcingfunction is applied to the battery at a first level and a firstmeasurement is obtained. The forcing function is applied at a secondlevel and a second measurement is obtained. The first and secondmeasurements are correlated to condition of the battery.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of a battery tester in accordancewith the present invention.

FIG. 2 is a simplified flow chart showing steps in accordance with oneembodiment of the present invention.

FIG. 3 is a graph of change in voltage versus state of charge (percent)for various values of differential current.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a simplified block diagram of battery monitoring circuitry 16in accordance with the present invention. Apparatus 16 is shown coupledto battery 12 which includes a positive battery terminal 22 and anegative battery terminal 24.

In a preferred embodiment, circuitry 16 operates, with the exceptionsand additions as discussed below, in accordance with battery testingmethods described in one or more of the United States patents obtainedby Dr. Champlin and Midtronics, Inc. and listed above. Circuitry 16operates in accordance with one embodiment of the present invention anddetermines the conductance (G_(BAT)) of battery 12 and the voltagepotential (V_(BAT)) between terminals 22 and 24 of battery 12. Circuitry16 includes current source 50, differential amplifier 52,analog-to-digital converter 54 and microprocessor 56. Current source 50provides one example of an adjustable forcing function for use with theinvention. Amplifier 52 is capacitively coupled to battery 12 throughcapacitors C₁, and C₂. Amplifier 52 has an output connected to an inputof analog-to-digital converter 54. Microprocessor 56 is connected tosystem clock 58, memory 60, and analog-to-digital converter 54.Microprocessor 56 is also capable of receiving an input from inputdevices 66 and 68. Microprocessor 56 also connects to output device 72.

In operation, current source 50 is controlled by microprocessor 56 andprovides a current I in the direction shown by the arrow in FIG. 1.Microprocessor 56 also controls the level (i.e., peak to peak, RMS,etc.) of the time varying component of the forcing function. In oneembodiment, this is a sine wave, square wave or a pulse. Differentialamplifier 52 is connected to terminals 22 and 24 of battery 12 throughcapacitors C₁ and C₂, respectively, and provides an output related tothe voltage potential difference between terminals 22 and 24. In apreferred embodiment, amplifier 52 has a high input impedance. Circuitry16 includes differential amplifier 70 having inverting and noninvertinginputs connected to terminals 24 and 22, respectively. Amplifier 70 isconnected to measure the open circuit potential voltage (V_(BAT)) ofbattery 12 between terminals 22 and 24 and is one example of a dynamicresponse sensor used to sense the time varying response of the battery18 to the applied time varying forcing function. The output of amplifier70 is provided to analog-to-digital converter 54 such that the voltageacross terminals 22 and 24 can be measured by microprocessor 56.

Circuitry 16 is connected to battery 12 through a four-point connectiontechnique known as a Kelvin connection. This Kelvin connection allowscurrent I to be injected into battery 12 through a first pair ofterminals while the voltage V across the terminals 22 and 24 is measuredby a second pair of connections. Because very little current flowsthrough amplifier 52, the voltage drop across the inputs to amplifier 52is substantially identical to the voltage drop across terminals 22 and24 of battery 12. The output of differential amplifier 52 is convertedto a digital format and is provided to microprocessor 56. Microprocessor56 operates at a frequency determined by system clock 58 and inaccordance with programming instructions stored in memory 60.

Microprocessor 56 determines the conductance of battery 12 by applying acurrent pulse I using current source 50. This measurement provides adynamic parameter related to the battery. Of course, any such dynamicparameter can be measured including resistance, admittance, impedance ortheir combination along with conductance. Further, any type of timevarying signal can be used to obtain the dynamic parameter. The signalcan be generated using an active forcing function or using a forcingfunction which provides a switchable load, for example, coupled to thebattery 12. The microprocessor determines the change in battery voltagedue to the current pulse I using amplifier 52 and analog-to-digitalconverter 54. The value of current I generated by current source 50 isknown and is stored in memory 60. In one embodiment, current I isobtained by applying a load to battery 12. Microprocessor 56 calculatesthe conductance of battery 12 using the following equation:$\begin{matrix}{{Conductance} = {G_{BAT} = \frac{\Delta \quad I}{\Delta \quad V}}} & \text{Equation~~1}\end{matrix}$

where ΔI is the change in current flowing through battery 12 due tocurrent source 50 and ΔV is the change in battery voltage due to appliedcurrent ΔI. Based upon the battery conductance G_(BAT) and the batteryvoltage, the battery tester 16 determines the condition of battery 12.Battery tester 16 is programmed with information which can be used withthe determined battery conductance and voltage as taught in the abovelisted patents to Dr. Champlin and Midtronics, Inc.

The tester can compare the measured CCA (Cold Cranking Amp) with therated CCA for that particular battery. Microprocessor 56 can also useinformation input from input device 66 provided by, for example, anoperator. This information may consist of the particular type ofbattery, location, time, the name of the operator. Additionalinformation relating to the conditions of the battery test can bereceived by microprocessor 56 from input device 68. Input device 68 maycomprise one or more sensors, for example, or other elements whichprovide information such as ambient or battery temperature, time, date,humidity, barometric pressure, noise amplitude or characteristics ofnoise in the battery or in the test result, or any other information ordata which may be sensed or otherwise recovered which relates to theconditions of the test how the battery test was performed, orintermediate results obtained in conducting the test. Additional testcondition information is provided by microprocessor 56. Such additionaltest condition information may include the values of G_(BAT) and batteryvoltage, the various inputs provided to battery tester 16 by theoperator which may include, for example, type of battery, estimatedambient or battery temperature, type of vehicle (i.e., such as providedthrough the Vehicle Identification Number (VIN) code for the vehicle) orthe particular sequence of steps taken by the operator in conducting thetest.

Typically, in prior art battery testers, current source 50 applied afixed current through application of a small fixed load. However, oneaspect of the present invention includes the recognition that theconductance, impedance, resistance or admittance measurements obtainedusing the aforementioned techniques can, in some instances, changedepending upon the size of current I used in obtaining the measurement.This change can be correlated, either experimentally or through modelingtechniques, to characteristics related to the condition of battery 12.Thus, microprocessor 56 obtains a number of data points and uses thosedata points to determine condition information of battery 12.

Although the embodiment illustrated in FIG. 1 shows a current source 50,element number 50 can be viewed as a forcing function and can be eitheran applied current, an applied load or an implied voltage. Typically, inprior art (non-load testers) the current I has been about 0.25 amp orthe applied resistance has been about 50 ohms.

In accordance with the present invention, a first forcing function isapplied and the resulting change in current or voltage from battery 12is measured by microprocessor 56 to determine a first data point(conductance, impedance, resistance, admittance, or their combination).Additional data points are then obtained, for example, by varying theforcing function a small amount, such as less than 10%. Other datapoints can be obtained by varying the forcing function from betweenabout 10% to about 50%. Yet further information can be obtained bychanging the forcing function by between 50% to about 100%, or greaterthan 100% such as orders of magnitude greater than the original forcingfunction. Note that these ranges are simply examples and other rangescan be used in accordance with the present invention. Further, anynumber of data points can be collected within a particular range, orspanning different ranges if desired and as determined based uponexperimentation. The particular percentages chosen are simply examplesand the invention is not limited to these values. In the broad sense,this aspect of the invention relates to comparing data measurementsobtained at different forcing function levels and the particular forcingfunction levels and their relationship to each other is not significant.However, in a more narrow aspect of the invention, the particularrelationship between the various forcing functions is significant andcan be used in determining the condition of the battery.

In another aspect of the present invention, the forcing function is notvaried, instead, a relatively high current level of between about 1 ampand about 100 amps is applied using a resistance of between 10 ohms andabout 0.1 ohms. Similarly, a relatively low current level between about0.1 amps and about 1 amp is applied using a resistance of between 100ohms and about 10 ohms. (Note that typical prior art load testers draw afixed current of about 100 to 200 amps using a fixed resistance of about0.12 ohms and 0.06 ohms).

The microprocessor uses the collected data to determine the condition ofthe battery. This information is correlated to various physicalattributes of the battery which can be determined experimentally. Forexample, the data can correlate to temperature, state of charge, gridcorrosion, loss of active material, sulfation, specific gravity,metallic degradation, polarization or stratification of battery 12.These or other determinations can be made based upon the measurementsmade at the different forcing function levels or through the use of asingle measurement obtained at a high or low forcing function level.

In yet another aspect of the present invention, measurement informationusing one measurement technique (conductance, impedance, resistance,admittance, or their combination) is used and correlated withmeasurement information obtained using a second measurement technique(conductance, impedance, resistance, admittance or their combination).This can be done at a single forcing function level or using the abovedescribed multiple level technique. The data from the differenttechniques can correlate to the condition of the battery. Further, morethan two techniques can be used in such a task.

FIG. 2 is a simplified flow chart 100 showing steps in accordance withone aspect of the present invention. At 102, the forcing function is setto a first level. At 104, a first measurement is obtained. At 106, theforcing function is set to a second level and a second measurement isobtained at 108. At 110, microprocessor 56 correlates the first andsecond measurements to a condition of the battery and, for example,provides an output on output 72 to an operator. As described above, morethan two different forcing function levels can be used in the presentinvention.

FIG. 3 is an example of a graph of differential voltage versus state ofcharge for various differential currents applied to battery 12, wherethe differential current levels have values of 0 Amps, 50 Amps, 100Amps, 500 Amps and 1000 Amps. As illustrated in FIG. 3, the resultantdifferential voltage ΔV is different for differing states of charge.FIG. 3 also illustrates that the ratio of ΔI/ΔV changes as a function ofΔI. This change in ΔI/ΔV, for various values of ΔI, can be correlated toother parameters which relate to battery 12.

The terms “inject” or “apply” is used herein to describe the supply ofvoltage or current either with active circuitry or by applying load tothe battery. Further, the applied signals can be time varying signalssuch as step functions, pulse signals, periodic signals, etc.

The present invention may be implemented using any appropriatetechnique. For simplicity, a single technique has been illustrateherein. However, other techniques may be used including implementationin all analog circuitry. Additionally, by using appropriate techniques,the battery resistance and a reference resistance (the reciprocal ofconductance) may be employed in the invention.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention. The present invention can be used withconductance, resistance, impedance, admittance or their combination inperforming the battery test.

What is claimed is:
 1. An electronic battery tester for determiningcondition of the storage battery, comprising: a four point Kelvinconnection adapted to electrically couple to the terminals of thebattery; an adjustable forcing function having a forcing function outputwith a time varying component having an adjustable level in response toan adjustment input, the forcing function output coupled to a first pairof connections of the Kelvin connection; a dynamic response sensorcoupled to a second pair of connections of the Kelvin connectionconfigured to provide a sensed output related to a time varying responseof the battery to the forcing function; digital circuitry coupled to theforcing function and the dynamic response sensor configured to providethe adjustment input to the forcing function whereby the forcingfunction output level is changed between a plurality of differentlevels, the digital circuitry configured to measure a dynamic parameterof the battery as a function of the sensed output at a plurality ofdifferent forcing function levels.
 2. The apparatus of claim 1 whereinthe digital circuitry is configured to correlate the dynamic parametersto a condition of the battery.
 3. The apparatus of claim 2 wherein thecondition comprises state of charge of the battery.
 4. The apparatus ofclaim 1 wherein the adjustable forcing function comprises a load.
 5. Theapparatus of claim 1 wherein the adjustable forcing function comprises acurrent sink.
 6. The apparatus of claim 1 wherein the dynamic responsesensor is configured to sense a voltage having a time varying component.7. The apparatus of claim 6 wherein the dynamic response sensor includesa differential amplifier.
 8. The apparatus of claim 1 including ananalog to digital converter configured to provide a digitalrepresentation of the sensed output to the digital circuitry.
 9. Theapparatus of claim 1 wherein the digital circuitry comprises amicroprocessor.
 10. The apparatus of claim 1 wherein the forcingfunction output comprises a square wave.
 11. The apparatus of claim 1wherein the dynamic parameter of the battery comprises conductance. 12.The apparatus of claim 1 wherein the dynamic parameter of the battery isselected from the group consisting of resistance, admittance andimpedance.
 13. A method of testing a battery, comprising: applying aforcing function having a time varying component at a first level to thebattery through a first pair of connections of a Kelvin connection;obtaining a first dynamic response measurement through a second pair ofconnections of the Kelvin connection related to a response of thebattery to the applied forcing function; applying the forcing functionhaving a time varying component at a second level to the battery throughthe first pair of connections of a Kelvin connection; obtaining a seconddynamic response measurement through the second pair of connections ofthe Kelvin connection related to a response of the battery to theapplied forcing function; and correlating the first and second dynamicresponse measurements to a condition of the battery.
 14. The method ofclaim 13 wherein applying the forcing function comprises applying a loadto the battery.
 15. The method of claim 13 wherein obtaining the firstand second dynamic response measurements comprises measuring dynamicvoltages of the battery.
 16. The method of claim 13 wherein correlatingthe first and second dynamic response measurements include determining adynamic parameter of the battery as a function of the applied forcingfunctions and dynamic response measurements.
 17. The method of claim 16wherein the dynamic parameter comprises conductance.
 18. The method ofclaim 16 wherein the dynamic parameter is selected from the groupconsisting of resistance, impedance and admittance.
 19. The method ofclaim 13 wherein the condition of the battery comprises state of chargeof the battery.
 20. The method of claim 13 wherein the forcing functioncomprises a square wave.
 21. The apparatus of claim 1 wherein theadjustable level comprises at least two current levels.
 22. The methodof claim 13 wherein the first and second levels of the forcing functioncomprise first and second current levels.